The invention relates to a blading for a gas turbine of an aircraft engine.
Various competing requirements must be taken into consideration in designing turbine blading of aircraft engines. In particular, a high efficiency should be achieved with low weight and low noise development. A wide variety of blading parameters influence each other, frequently in a highly nonlinear manner, so that analytically a corresponding optimization is hardly possible.
A blade row of a steam turbine is known from German Patent Document No. DE 10 2008 031 781 A1. The document cites for this distribution ratios between 0.85 and 1.1 in connection with downstream flow angles of a maximum 159° as known. Gas turbines of aircraft engines are not considered.
The present invention provides an improved blading.
An arrangement of moving blades and/or an arrangement of guide blades, in particular of one or more stages, is described as blading within the meaning of this invention. A blading according to the invention is particularly suited for high-speed gas turbines, especially high-speed low-pressure gas turbines, in aircraft engines. In a preferred embodiment, an aircraft engine has a blading according to the invention.
Some or all blades of the blading, meaning in particular some or all guide and/or moving blades of one or more stages, preferably have a distribution ratio in a section near the tip of at least 0.70 and in particular at least 0.9.
As a section near the tip, a section is described that lies near the blade tips of the moving blades, i.e., radially outside, or forms the blade tip as TIP section. Correspondingly, as a section near the root, a section is described that lies near the blade roots of the moving blades, i.e., radially inside, or defines the blade root. In particular, within the meaning of this invention a section that lies radially above a center of a radial blade height, and preferably a section in the area between 95% and 100% of the moving blade height, is described as a section near the tip, and a section that lies radially below this blade height center and preferably in the area between 0% and 5% of the moving blade height is correspondingly described as a section near the root. With both moving and guide blades, a section close to the tip correspondingly lies radially farther from a rotation axis of the turbine rotor than the blade height center, which in turn is radially farther from the rotation axis than a section near the root. In particular, a section within the meaning of this invention can lie at a radially constant height or along a flow line, i.e., with a convergent or divergent flow channel run radially inward or outward. As the blade root, the lower limit of the blade in particular is described here, the so-called platform, whereas a fastening area afterwards as necessary, which occasionally is likewise described as a blade root, is not considered since this invention deals with an optimization of the blade and the flow influenced by it.
As is standard practice, the distribution ratio is understood in particular as the quotient of a blade pitch, i.e., the distance between two blades in the circumferential direction, divided by the chord length of the blade between the blade front and rear edges.
The distribution ratio in a section near the tip of some or all blades of the blading, meaning in particular some or all guide and/or moving blades of one or more stages, preferably is at most 0.97, in particular at most 0.95. Together with the parameters according to the invention explained below, these preferred upper and lower limits for the distribution ratio in particular yield light and/or low-noise bladings with high efficiencies for aircraft engines.
According to a first aspect of this invention, a downstream flow angle of some or all blades of the blading, meaning in particular some or all guide and/or moving blades of one or more stages, at most amounts to 167°, preferably at most 165°, and at least 155°, preferably at least 160°.
As is standard practice, downstream flow angle is understood in particular as the larger of the two complementary angles between the theoretical downstream flow speed or the tangent on the suction or pressure side on the blade rear edge on the one hand and the blading circumference or a normal level to the rotation axis of the turbine on the other. The upper and lower limits according to the invention relate to the amount of the downstream flow angle, i.e., without consideration of the orientation between rotation and downstream flow direction.
If we subtract from the downstream flow angle of 90° given according to the invention, the result is the angle between the theoretical downstream flow speed or the tangent on the suction or pressure side on the blade rear edge on the one hand and the rotation axis of the turbine on the other, which occasionally is likewise defined as downstream flow angle. According to the first aspect of the present invention, this differently defined downstream flow angle accordingly amounts to at most 77°, preferably at most 75°, and at least 65°, preferably at least 70°.
According to a second aspect of this invention, which preferably can be combined with the first aspect, an acceleration ratio amounts to at least 1.4 and in particular at least 1.5. As is standard practice, acceleration ratio is understood in particular as the quotient of the amount of the theoretical downstream flow speed divided by the amount of the theoretical upstream flow speed. For example, from the mass continuity condition an estimate can be made for the channel sections between adjacent plates between channel entry and channel exit, i.e., the narrowest channel section.
The acceleration ratio can be constant over the radial blade height. In a preferred embodiment, however, in a section near the root or on the hub it is at least 1.4, in particular at least 1.5, and grows larger in the direction toward a section near the tip, preferably by a factor greater than or equal to 2.
The theoretical upstream and downstream flow speed results from the blade geometry and the fluidic boundary conditions, especially design, normal or reference operating points. The theoretical upstream and downstream flow speed can describe the vectorial speed including a radial component or also just the axial and circumferential components of a three-dimensional flow; the theoretical upstream or downstream flow speed can therefore have two (axial, circumferential-direction) or three (radial, axial and circumferential-direction) components.
Through the invention's parameter combination of upper and/or lower limit for the distribution ratio, the downstream flow angle and/or the acceleration ratio, an equally light and/or low-noise blading with a high efficiency can be provided, and particularly in a high-speed low-pressure turbine (stage).
In a preferred embodiment, some or all moving blades of one or more stages in a section near the tip have a maximum profile thickness of at most 2.5 mm and preferably at most 2 mm if these moving blades are formed as full solid blades. For hollow blades, a maximum profile thickness in a section near the tip preferably is at least 4.5 mm and at least 4 mm is preferred. With sufficient sturdiness, taking into consideration the load capacity of the blade material and depending on the material temperature, a light blading can therefore be presented.
Preferably, some or all guide blades of one or more stages in a section of the tip have a maximum profile thickness of at most 10 mm and preferably at most 9 mm. Advantageously, the guide blades are formed as full solid blades. The limitation of the maximum profile thickness advantageously takes into account the thermal fatigue.
In a preferred embodiment, some or all moving blades of one or more stages have at least one seal tip, preferably two or more seal tips each. Advantageously, an abradable lining on the turbine housing is arranged radially opposite the tips.
Preferably, the degree of reaction of a blading according to the invention is at least 0.35 and preferably at least 0.4. In addition, or alternatively, the degree of reaction is at most 0.6 and preferably at most 0.55. As is standard practice, degree of reaction can be defined in particular as the ratio of the enthalpy converted into flow energy and mechanical work in the moving blades of a turbine stage to the total, in particular isentropic enthalpy gradient of the turbine stage. Equally, the degree of reaction within the meaning of this invention can be defined by the so-called pressure degree of reaction that gives the ratio of the specific flow work in the rotor to the specific flow work between stage entry and exit. Depending on approximation of the static change of state by a polytrope or isentrope and isobar, this can involve in particular the polytropic or isotropic pressure degree of reaction. Preferably, the degree of reaction is formed with the static pressures and results as the quotient of the difference of the static pressure in the moving row divided by the difference of the static pressure in the entire stage from guide and moving rows.
In a preferred embodiment, the profile sections are threaded radially over the center of gravity, which yields a favorable blading in terms of design, flow, and structural mechanics. A slight axial offset of the profile section, meaning an axially slightly beveled blade, is also understood as threaded radially over the center of gravity within the meaning of this invention.
Preferably, a theoretical stagnation point flow line meets the blade profile in the area of the front edge radius. The theoretical stagnation point flow line is defined in particular by the flow line ending in the stagnation point in a theoretical design flow.
In a preferred embodiment, the rotational frequency of moving blades of the blading in one or more noise work points is at least 6000 Hz, in particular at least 6300 Hz. The nominal speed in a noise work point and the minimum rotational frequency yield the minimum necessary moving blade number of such a preferred embodiment. As is standard practice, a noise work point for an aircraft engine can be defined in a specification, and in particular specify an altitude, speed, and the like.
Further features and advantages result from the detailed description and Figures.